The most common and most likely answer to this crossword clue is the 12 letter word ALEXANDRINES
I've seen this crossword clue in The Times
A
L
E
X
A
N
D
R
I
N
E
S
Buddy explains!
The straight part
We know that "lines" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lines = alexandrines.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ALEXANDRINES mean?
ALEXANDRINES noun- A line of poetic meter having twelve syllables, usually divided into two or three equal parts.
- An Alexandrine parrot or parakeet.